ASTM D4192-15

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Designation: D4192 − 08 D4192 − 15
Standard Test Method for
Potassium in Water by Atomic Absorption
Spectrophotometry
This standard is issued under the fixed designation D4192; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This test method covers the determination of low amounts of potassium in waters having low solids content. The applicable
range of this test method is 0.20 to 4.0 mg/L when using the 766.5-nm resonance line. The range may be extended upward by
dilution of an appropriate aliquot of sample or by using the less-sensitive 404.4-nm resonance line. Many workers have found that
this test method is reliable for potassium levels to 0.02 mg/L, but use of this test method at this low level is dependent on the
configuration of the aspirator and nebulizer systems available in the atomic absorption spectrophotometer as well as the skill of
the analyst. The precision and bias data presented are insufficient to justify use of this test method in the 0.02-mg/L range.
1.2 This test method has been used successfully with spiked reagent water. It is the analyst’s responsibility to ensure the validity
of this test method to other low dissolved solids matrices.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this The values
given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not
considered standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. For a specific precautionary statement, see Note 38.6.
2. Referenced Documents
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D4841 Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
D5810 Guide for Spiking into Aqueous Samples
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
3. Terminology
3.1 Definitions: For definitions of terms used in this test method, refer to Terminology D1129.
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D1129.
4. Summary of Test Method
4.1 Potassium is determined by flame atomic absorption spectrophotometry. The potassium content is determined by aspirating
the low solids sample directly with no sample pretreatment.
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved Oct. 1, 2008Feb. 1, 2015. Published October 2008March 2015. Originally approved in 1982. Last previous edition approved in 20032008 as
D4192 – 03.D4192 – 08. DOI: 10.1520/D4192-08.10.1520/D4192-15.
Platte, J. A., and Marcy, V. M., “A New Tool for the Water Chemist,” Industrial Water Engineering, May 1965 .
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4192 − 15
5. Significance and Use
5.1 Potassium occurs in rocks in a form that is not easily solubilized; therefore, the potassium content of natural waters is
usually low. Most natural waters contain less than 20 mg/L of potassium, but waters containing several hundred milligrams per
litre are occasionally found. Potassium is essential to animal nutrition, but a concentration of 1000 to 2000 mg/L in stock water
is regarded as the extreme limit permissible.
6. Interferences
6.1 In the analysis of low-solids water, interferences are usually negligible.
7. Apparatus
7.1 Atomic Absorption Spectrophotometer for use at 766.5 nm.
NOTE 1—The manufacturer’s instructions should be followed for all instrumental parameters. Wavelengths other than 766.5 nm may be used only if
they have been determined to be equally suitable.
7.2 Potassium Hollow-Cathode Lamps—Multielement hollow cathode lamps are available and also have been found
satisfactory.
7.3 Pressure-Reducing Valves—The supplies of fuel and oxidant shall be maintained at pressures somewhat higher than the
operating pressure of the instrument by using suitable valves.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
8.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to
Specification D1193, Type I. Other reagent water types may be used provided it is first ascertained that the water is of sufficiently
high purity to permit its use without adversely affecting the bias and precision of the test method. Type II water was specified at
the time of round robin testing of this test method.
8.3 Potassium Solution, Stock (1.0 mL = 1.0 mg K)—Dry potassium chloride to constant weight at 105°C. Dissolve 1.907 g of
the dry potassium chloride (KCl) in water and dilute to 1 L with water.
NOTE 2—Certified potassium stock solutions of appropriate known purity are commercially available through chemical supply vendors.
8.4 Potassium Solution, Standard (1.00 mL = 0.1 mg K)—Dilute 100.0 mL of potassium stock solution to 1 L with water.
8.5 Oxidant: Air, which has been passed through a suitable filter to remove oil, water, and other foreign substances is the usual
oxidant.
8.6 Fuel: Acetylene—Standard, commercially available acetylene is the usual fuel. Acetone, always present in acetylene
cylinders can affect analytical results. The cylinder should be replaced at 50 psig (345 kPa)345 kPa (50 psig) to avoid acetone carry
over. (Warning—“Purified” grade acetylene containing a special proprietary solvent rather than acetone should not be used with
poly(vinyl chloride) tubing as weakening of the tubing walls can cause a potentially hazardous situation.)
NOTE 3—Warning: “Purified” grade acetylene containing a special proprietary solvent rather than acetone should not be used with poly(vinyl chloride)
tubing as weakening of the tubing walls can cause a potentially hazardous situation.
9. Sampling
9.1 Collect the samples in accordance with the applicable ASTM standard as follows: Practices D3370 and Practice D1066.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
TABLE 1 Determination of Bias for Potassium in Reagent Water
by Atomic Absorption
Amount Amount
Added, Found, S S Bias %
t o
mg/L mg/L
0.15 0.164 0.037 0.014 + 9.33
1.50 1.62 0.085 0.044 + 8.00
3.00 3.03 0.179 0.062 + 1.13
D4192 − 15
10. Standardization
10.1 Prepare 100 mL each of a blank and at least four standard solutions to bracket the expected potassium concentration range
of the samples to be analyzed by diluting the standard potassium solution 8.4 with water. Prepare the standards each time the test
is to be performed. performed or as determined by Practice D4841. Select the standards to give zero, median, and maximum points
for an analytical curve.
10.2 Analyze at least four working standards containing concentrations of potassium that bracket the expected sample
concentration, prior to analysis of samples, to calibrate the instrument. Aspirate the blank and the standards and record the
instrument readings. Aspirate water between standards.
10.3 Prepare an Read directly in concentration if this capability is provided with the instrument or prepare a linear analytical
curve by plotting the absorbance versus concentration for each standard on linear graph paper. Alternatively, read directly in
concentration if this capability is provided with the instrument.
11. Procedure
11.1 Aspirate each sample and determine its absorbance or concentration. Aspirate water between samples.
12. Calculation
12.1 Calculate the concentrations of potassium in the samples, in milligrams per litre, by either reading directly in concentration
if the capability is provided with the instrument or referring the absorbance obtained for each sample to a prepared analytical curve
10.3(see 10.3or reading directly in concentration if the capability is provided with the instrument.).
12.2 If an aliquot of diluted sample was analyzed, multiply the concentration of potassium, in milligrams per litre, by the
appropriate diluti
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